Try to improve your lighting. My guess is your
standing to close to your green screen.

What you’re seeing {What it looks like to me} is shadows being cast by you.
Behind you on the green screen.
And green light reflecting back on you. As an overcast effect, on the outside
of your shirt. A green screen will cast green light back upon you. Especially when
lit to brightly, and your standing in too close proximity.

You’re going to be limited as to how far you can stand away from your green
screen, based upon its size. Ideally, you should be a minimum of four feet from
the screen or further.

You want to have soft, diffused lighting falling on the
screen. And yourself as well.

You want just enough light falling on you from all
directions. So that you’re not casting shadows upon yourself. Or the screen
behind you.

This is easier said than done. But has a lot to do with
whether or not you’re going to have good results.

However, the remove a color feature in Camtasia. While it is
capable of doing a decent job. It is not a high level high quality chroma key
filter. So you should set your expectations levels accordingly. Expect Less-than-perfect
results. That way you don’t chase your tail until you acquire perfect results.

In the example below I’m using a pretty good lighting set up
and a proper Muslim green screen cloth.

Then with the footage placed in Camtasia 2018. With the
settings optimized/adjusted to the best results I could acquire. The edges surrounding
me are quite jagged. There’s also green fringing that cannot be alleviated as
well.

Getting first-class results, with a standard DSLR like I
used. Can be somewhat challenging. Even with high-end video editors.

However, results are far more acceptable coming out of a program
like Premier Pro.

I’m including this image from Premier Pro for Demonstration/Comparison
purposes.

In summary, getting a good clean result when doing green
screen work. Can be quite challenging under the best of conditions. If you’re
shooting in a studio while using a camera that cost several thousand dollars,
your results will improve. Most of us are not in that position.